Photo: The surface of a lotus leaf is hydrophobic. The leaf is shaped such that droplets of water that fall on it pick up dirt as they roll off the leaf, cleaning the plant. Now researchers have shown a similar effect on a graphene surface. Courtesy of sxc.hu.

In recent research performed at the Rensselaer Polytechnic Institute, scientists have shown that covering a rough surface with a layer of graphene reduces the sticking of water droplets on that surface. As opposed to bare rough surfaces on which water tends to pin to the crevices, a graphene-coated surface is smooth and hydrophobic, allowing water droplets to glide away from the material, similar to the lotus leaf effect found in nature. For their research, published in the journal ACS Nano, the researchers used a monolayer graphene sheet grown by chemical vapor deposition (CVD) and transferred to the target rough surface using a polymer film. The CVD growth process and graphene transfer are Graphenea's specialties, and if you wish to have large-area high-quality graphene on a custom substrate, please contact us by email.

Interestingly, also recently, scientists at the US Naval Research Lab (NRL) have shown that they can guide water droplets in a desired direction on a graphene surface. This new achievement offers potential applications ranging from electronics to mechanical resonators to bio/chemical sensors. For example, the ability to guide small amounts of liquids to a desired location on a chip is the motivation of the burgeoning technology of microfluidics. Microfluidic chips are being used as biosensors for various diseases, and can be used as sensors for dangerous chemicals. In the work performed at NRL, also published in ACS Nano, the graphene surface was modified with a chemical gradient, induced by a clever modification of plasma-doping. The chemical gradient also creates a potential gradient which pulls the droplets in a pre-specified direction. It will be interesting to see whether this work can be extended to dynamical gradients through, for example, electrostatic gating. Such research would open up the way to real-time control of the motion of liquids on a surface.

Both mentioned works used high-speed cameras to record the motion of water on graphene, and ACS Nano offers open access to the “supplementary information” section where you can see the cool movies.